This invention relates to an electric field sensor for measuring an electric field intensity of a signal which is an electromagnetic wave propagating through a space.
FIG. 1 is a front view showing a main portion of a conventional electric field sensor. The electric field sensor comprises a reception antenna 101, an electric field sensor head 102, an incident optical fiber 103, an outgoing optical fiber 104, a light source (not shown), and an optical detector (not shown).
The reception antenna 101 is responsive to an input signal. The electric field sensor head 102 is for varying a light intensity of a propagating light beam propagating therethrough in response to an electric field intensity of the input signal received by the reception antenna 101. The incident and the outgoing optical fibers 103 and 104 are connected to the electric field sensor head 102. The light source is connected to one end of the incident optical fiber 103 and is for emitting a light beam to the incident optical fiber 103 as the propagating light beam. The optical detector is supplied with the propagating light beam delivered from the electric field sensor head 102 through the outgoing optical fiber 104 and detects the propagating light beam.
The electric field sensor head 102 comprises a substrate 105, an incident optical waveguide 106, two phase-shift optical waveguides 107, an outgoing optical waveguide 108, and modulation electrodes 109. The incident optical waveguide 106 is formed on the substrate 105 to be connected to the incident optical fiber 103. The phase-shift optical waveguides 107 are formed on the substrate 105 to be branched from the incident optical waveguide 106. The outgoing optical waveguide 108 is formed on the substrate 105 to be connected at one end to the outgoing optical fiber 104 and at the other end to the junction of the two phase-shift optical waveguides 107. The modulation electrodes 109 are formed in the vicinity of the two phase-shift optical waveguides 107, respectively, and are connected to the reception antenna 101.
The above described electric field sensor has a low sensitivity.